Due to rapidly increasing traffic in optical communications in recent years, the transmission capacity of presently used single-core optical fibers is approaching its limit. So, as a means to further expand the communication capacity, multicore fibers in which a plurality of cores are formed in one fiber have been proposed.
When a multi-core fiber is used as a transmission path, each of the core parts of the multicore fiber needs to be connected to corresponding core parts of another multicore fiber, other optical fibers, an optical element, or the like respectively to send and/or receive transmission signals. As a method for connecting such a multicore fiber and a single core fiber, Patent Document 1 discloses a method in which a multicore fiber is connected with a bundle fiber, in which single core optical fibers are arranged at the positions corresponding to the core parts of the multicore fiber, to send and/or receive transmission signals.
Meanwhile, multicore fibers having cores arranged in a plurality of rows as a lattice for a use in data centers and the like, for example, have been suggested. Thus, a fan out mechanism that can be connected to such multicore fibers has been in demand.
As a fan out mechanism, there is a method in which a multi-hole capillary having multiple-string holes is used, for example. An optical fiber is inserted into each of the holes of the capillary and fixed so that the optical fibers can be arranged at predetermined positions.
However, in such a multi-hole capillary, there may be some variations in hole diameter and hole pitch of about ±2 to 3 μm. This precludes realization of the required dimension accuracy (±1 μm or less) of the hole positions and the like.
Also, since it is difficult to make the outer diameter of a multicore fiber too large for issues such as bending allowance, it is necessary that the pitch of the cores in the multicore fiber is as narrow as approximately 40 to 50 μm. However, the thickness of the wall between adjacent holes in a multi-hole capillary is required to be 20 μm at the minimum, and thus, taking the wall thickness into consideration, the hole diameter is required to be approximately 20 to 30 μm. Thus, the diameter of the fiber to be used must be equal to or less than the hole diameter. However, such an optical fiber with a thin diameter is too thin and is difficult to handle with.